1. Field of the Invention
The invention relates to the layout design and mounting and dismounting of a circuit substrate in an electronic apparatus such as, for example, a printer or a copying machine.
2. Description of the Related Art
In recent years, there have been popularized image forming apparatuses such as printers and copying machines using an electrophotographic process which can output a full-color image.
Description will hereinafter be made with reference to the accompanying drawings. FIG. 5 shows an example of the construction of the essential portions of a conventional full-color printer. A photosensitive drum (hereinafter simply referred to as the photosensitive member) 1 as an image bearing member is provided so as to be rotatable in the direction indicated by the arrow A by a motor (not shown). Around the photosensitive member 1, there are disposed a primary charging device 7a, an exposing apparatus 8, a developing unit 13, a transfer roller 10 and a cleaner apparatus 12.
The developing unit 13 has four developing apparatuses 13Y, 13M, 13C and 13K for full-color developing. The developing apparatuses 13Y, 13M, 13C and 13K develop a latent image on the photosensitive member 1 with yellow (Y), magenta (M), cyan (C) and black (K) toners. When the latent image is to be developed with the toner of each color, the developing unit 13 is rotated in the direction indicated by the arrow R by a motor (not shown), and the developing apparatus of that color is positioned so as to come into contact with the photosensitive member 1.
The toner images of the respective colors developed on the photosensitive member 1 are successively transferred to a belt 2 as an intermediate transfer member by the transfer roller 10, and the toner images of the four colors are superimposed one upon another. The belt 2 is stretched over rollers 17, 18, 19 and 20. Of these, the roller 17 functions as a drive roller coupled to a drive source (not shown) and driving the belt 2, and drives the belt 2 in the direction indicated by the arrow B. The roller 19 functions as a tension roller for adjusting the tension of the belt 2, and the roller 20 functions as a backup roller for a transfer roller 21.
A belt cleaner 22 is provided at a location opposed to the roller 17 with the belt 2 interposed therebetween, and any residual toners on the belt 2 are scraped off by a blade.
A recording sheet drawn out of a recording sheet cassette 23 or 24 to a conveying path by a pickup roller 25a or 26a and a pair of separating rollers 25b or 26b is directed to a pair of registration rollers 29 by a pair of rollers 27 or 28. The recording sheet once stopped at the nip portion of the pair of registration rollers 29 is fed to a secondary transfer nip portion, i.e., the portion of contact between a secondary transfer roller 21 and the belt 2, in timed relationship with the toner images on the belt 2. The toner images formed on the belt 2 are transferred onto the recording sheet at this nip portion, and are heat-fixed by a fixing apparatus 5, and the recording sheet is discharged to a tray 30.
In the color printer of the above-described construction, an image is formed in the following manner. First, a voltage is applied to the charging device 7a to thereby minus-charge the surface of the photosensitive member 1 uniformly at predetermined charging portion potential. Subsequently, the exposing apparatus 8 including a laser scanner or the like scans the photosensitive member 1 by a laser beam modulated in accordance with an image signal, whereby a latent image corresponding to an image is formed.
A developing bias preset for each color is applied to the developing roller of the developing apparatus 13Y or the like, and the latent image formed on the photosensitive member 1 is developed with a toner when it passes the position of the developing roller, and is visualized as a toner image. The toner image is transferred to the belt 2 by the transfer roller 10, and a toner image of a first color is formed on the belt 2. This operation is repeated four times (correspondingly to the four colors), whereby toner images of the four colors are formed on the belt 2. At that time, the transfer roller 21 as a secondary transfer apparatus is spaced apart from the belt 2 by a mechanism (not shown) for moving it toward and away from the belt. The belt cleaner 22 is also spaced apart from the belt 2 by a mechanism (not shown) for moving it toward and away from the belt.
After the toner images of the four colors have been transferred and immediately before the leading edge of the toner images comes to the position of the roller 20, the secondary transfer roller 21 is brought into contact with the belt 2 by the mechanism for moving it toward and away from the belt, and the toner images are transferred to the recording sheet at the nip portion thereof. The recording sheet to which the toner images have been transferred is fed to the fixing apparatus 5, whereby the toner images are fixed as a full-color image. Any toners residual on the photosensitive member 1 are removed and collected by the cleaner apparatus 12 and lastly, the photosensitive member 1 is charge-eliminated uniformly to the vicinity of 0 volt by a charge eliminating apparatus 7b, and becomes ready for the next image forming cycle.
In such an image forming apparatus, there are carried a plurality of electric cables for effecting the exchange of electric power and data among various electric circuit substrates for controlling various operations.
These electric circuit substrates include an AC power source circuit substrate for introducing electric power from a commercially available AC power source, a high voltage source circuit substrate for generating a high voltage for forming a toner image on the image bearing member, a DC power source circuit substrate for driving a motor or the like, and a control circuit substrate for controlling the driving of these circuits. Also, the above-described plurality of circuit substrates are connected together by cables for electrical energization.
The installation places of the electric circuit substrates exist at all locations in the image forming apparatus from the use and the positional relation or the like with other parts, and along therewith, the cables connecting the substrates together are also installed at all locations in the image forming apparatus.
In such an electrical arrangement using a plurality of cables, the distance between the AC component cable and the DC component cables is short and therefore, noise may shift from the AC component cable to the DC component cable to thereby give rise to the problem of adversely affecting the formed image or spoiling the stable operation of the apparatus. Also, in the DC component cable, a great deal of noise occurs from the circuit substrate transmitting and receiving data of a high clock.
At present, as a countermeasure for this, there is used a countermeasure adopting a cableless connecting method of providing a covering material for electrically shielding the surfaces of the cables, or extending the cables at such an arrangement that the distance between the AC cable and the DC cable becomes long, or directly connecting respective connectors installed on the circuit substrates.
As an example, the invention described in Japanese Patent Application Laid-Open No. 2001-238045 achieves a reduction in noise by covering a harness (flat cable) which is a noise causing source with a shield member exclusively therefor.
Also, in the conventional image forming apparatus, in order to accurately hold a unit concerned in image forming, including these electric members, two pairs of large metal plates are used to form a frame (side plates).
However, the method of providing a covering material for electrically shielding the surfaces of the cables as in the above-described example of the conventional art leads to a great increase in cost, and the method of extending the cables so that the distance between the AC cable and the DC cable may become long results in the greater lengths of the AC cable and the DC cable or the complication of wiring, thus reducing the maintenance property of other parts.
Also, the method of directly connecting the respective connectors installed on the circuit substrates has resulted in the aggravation of the working property during assembly because the circuit substrates are connected together, and thereafter are assembled to an apparatus main body.
Also, as regards supporting plates, metal plates of substantially the same size as that of the image forming apparatus have been used and this has caused the bulkiness (increased cost) of a molding machine and an increase in conveying cost.